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在研究双向压缩条件下压剪复合型裂纹应力分布特征及断裂破坏机制基础上,考虑渗透压对初始裂隙面上有效正应力的影响,提出高低渗透压环境的判定准则,并基于滑动裂纹模型理论及最大周向拉应力破坏准则,得到不同渗透压环境下初始裂隙尖端微裂纹起裂特征与规律。研究结果表明:压剪复合应力条件下,初始裂隙尖端发育微裂纹的最优倾角与裂隙面摩擦系数直接相关,随裂隙面摩擦系数的增大,最优初始裂隙倾角由45°起逐渐增大;低渗透压条件下,渗流场的存在使裂纹面摩擦系数发生弱化,进而使得最优初始裂隙倾角向45°靠近,而渗透压直接降低裂隙面上有效正应力且与裂隙倾角无关,其仅仅影响裂隙体材料的初裂强度;高渗透压条件下,初始裂隙面由压剪复合应力状态转化为拉剪复合应力状态,并在拉剪复合应力场作用下,尖端微裂纹起裂角随KI/KII的不断增大,由70.5°逐渐趋近于0°。
Based on the study of the stress distribution characteristics and fracture failure mechanism of the compression-shear type composite cracks under the bidirectional compression, the criterion of the osmotic pressure on the effective normal stress on the initial fracture surface is taken into account and the criteria of the high and low osmotic pressure environments are proposed. Based on the theory of the sliding crack model And the maximum circumferential tensile stress failure criterion, the characteristics and regularities of initiation of microcracking at the initial crack tip under different pressures are obtained. The results show that the optimum inclinations of the initial crack tip microcracks are directly related to the friction coefficient of the fracture surface under the condition of the compressive shear stress. With the increase of the friction coefficient of the fracture surface, the optimum initial fracture angle increases gradually from 45 ° Under the condition of low osmotic pressure, the seepage field weakens the friction coefficient of the crack surface, so that the optimal initial fracture angle approaches 45 °, while the osmotic pressure directly reduces the effective normal stress on the fracture surface and has no relation with the fracture inclination. Under the condition of high osmotic pressure, the initial fracture surface is changed from compressive-shear composite stress state to tensile shear-shear complex stress state. Under the action of tensile-shear composite stress field, the initiation angle of tip micro-cracks changes with KI / KII increasing, gradually approaching 0 ° from 70.5 °.